The use of disposable patterns consisting of films is known from German Offenlegungsschrift No, 1,926,163. These patterns can be produced in a simple manner by a known deep-drawing shaping process utilising reduced or elevated pressure. The patterns are introduced into a mounding box, whereupon the latter is filled with loose binderless sand. The sand is thereupon subjected to reduced pressure, so that the film of the pattern is pressed against the sand by the external air pressure. In this way it is possible to produce patterns of stable shape from very thin films. This stability of shape is however ensured in the case of thin films only as long as the reduced pressure is maintained in the sand. This method of casting has been found decidedly advantageous because the production of the patterns entails only little expense, a casting having a very smooth surface is obtained, and the preparation of the sand is not necessary. In order to remove the casting from the mould all that is necessary is to terminate the reduced pressure in the sand.
A prerequisite for the performance of the process described above is that the reduced pressure in the upper and lower parts of a two-part moulding box should be maintained from the completion of the pattern until the casting has been completely cooled. To this end it is known for the upper and lower boxes each to be provided with a flexible reduced pressure pipe. By means of these pipes a reduced pressure is maintained in both halves of the moulding box from the completion of the mould until the casting is removed from the mould.
For continuous production purposes the moulding boxes are placed on trucks of a closed-circuit rail conveyor which brings the moulding boxes to the various stations. The transfer of the moulding boxes, which are continuously connected to flexible reduced pressure pipes, is effected with the aid of gripping devices such as are described, for example, in the periodical "Giesserei 60" (1973) No. 21, page 664. The cycle sequence in which a rail conveyor of this kind can work depends on its length, that is to say on the number of rail conveyor trucks. The length of these known rail conveyors is above all limited by the reduced pressure pipes which are connected to the moulding boxes and which have been found to be a considerable hindrance. It is known for a rail conveyor of this kind to be made circular and for all the reduced pressure pipes leading to the moulding boxes to be connected to a centrally disposed reduced pressure pipe. A substantial disadvantage of the mould boxes continuously connected to the reduced pressue pipes is that manipulation thereof is restricted. If the moulding boxes are placed on rail conveyor trucks which are moved in timed sequence, the upper and lower boxes must be produced, brought together, and placed on the rail conveyor truck within a determined cycle time. This means that the time required for the production of the moulding boxes is also a decisive factor for the cycle times.
It is substantially more advantageous for the rail conveyor trucks to be provided with their own reduced pressure pipe connecting the rail conveyor trucks to one another. When the moulding boxes are placed on the trucks, they are then connected to the reduced pressure pipe of the trucks, so that the reduced pressure pipes connected to the moulding boxes during their manufacture can then be removed. A rail conveyor constructed in this manner has the advantage that it can be made in any desired length, since the reduced pressure pipe connected to the rail conveyor trucks has to be connected to a central reduced pressure pipe only at one point in each case. Another advantage is that the moulding boxes can be produced independently of the rail conveyor.
It is an object of the invention to provide an apparatus of the kind first mentioned above, with the aid of which casting moulds can be produced with the aid of binderless sand subjected to a reduced pressure, while maintaining the vacuum, and, for example, transferred to a rail conveyor.
According to the invention there is provided an apparatus for producing and transferring casting moulds utilising binderless sand subjected to a reduced pressure, said apparatus comprising a travelling gripper which is arranged to be raised and lowered and which is provided with two couplings to hold a moulding box, said couplings being rotatable about a horizontally extending axis, and one coupling being connected to a vacuum pipe for evacuating the moulding box. The coupling provided with the vacuum pipe acts on a projection which is provided on the moulding box and is connectable to the evacuation pipe of the latter. By means of this coupling the vacuum can be produced and maintained in the moulding box. Since with the aid of the apparatus of the invention both the lower part and the upper part of a moulding box can be produced, and the two parts can be brought together and placed on the rail conveyor, the apparatus makes it possible for the moulding boxes to be turned, transported, and deposited.
According to an advantageous embodiment of the invention, one of the two couplings is connected to means operable to rotate the moulding box about said horizontally extending axis. The said means advantageously comprises a toothed rack provided on a piston rod, and a pinion connected to the other of the couplings. The rotary drive is so designed that pivot movements through 180.degree. are possible. For the hoorizontal displacement of the two couplings use is made of a double-action hydraulic cylinder.